The dinoflagellate cyst is an important stage in the life history of dinoflagellate, it can not only promote the outbreak of red tide, but also help the dinoflagellate to survive from an unfavorable environment. According to the ecological, economic and human health effects, the dinoflagellate cysts can be divided into harmful dinoflagellate cysts (e.g. most Alexandrium) and harmless dinoflagellate cysts (e.g., most of the original polychaete). According to whether the dinoflagellate—produce toxins, the harmful dinoflagellate cysts can be divided into harmful toxin-producing dinoflagellate cysts (such as Alexandrium tamarense cyst, with thorn knee gully cyst and Prorocentrum cyst) and harmful no-toxin-producing cyst (can cause red tide, such as Scrippsiella trochoidea, Polykrikos kofoidii and Polykrikos schwartzii, etc.). According to the type of toxins contained and the hazards they cause to humans, harmful toxin-producing dinoflagellate cyst can be divided into different types, such as toxins (PSP) contained in the cyst of Alexandrium tamarensis causing the appearance of limbs numbness, speech impairment and other symptoms of paralysis, Procentrum lima contains the toxin (NSP) can cause diarrhea, etc. in humans. Therefore, the accurate identification of dinoflagellate cyst is very important. It is not only conducive to the monitoring of harmful red tide to reduce the harm caused by harmful red tide, but also conducive to the study of dinoflagellate diversity.
The identification of dinoflagellate cysts are mainly divided into morphological identification and molecular biological identification.
Morphological identification, including cyst morphology identification and morphological identification of vegetative cells after germination, according to the morphological characteristics, majority of morphological characteristics can be identified to the genus level, a few of morphological characteristics can be identified to the level of species, and identification through the germination of cyst needs a longer time, and not all cyst can germinate successfully;
Molecular biological identification is mainly based on molecular barcodes. Since barcodes in databases such as NCBI are constantly improved, so that molecular barcodes have been widely used in the field of identification of dinoflagellate cyst, and most of them can be identified to species level.
The traditional molecular identification of dinoflagellate cyst often requires the germination and proliferation of dinoflagellate cyst for the purpose of extracting nucleic acids, then the remaining experimental steps for molecular identification can be carried out. The disadvantage of this molecular identification method is time-consuming and not conducive to the rapid identification of dinoflagellate cyst, and is not suitable for ungerminated cyst and the cyst with low abundance cyst. Although Bolch et al. (2001) invented the method for molecular identification of single dinoflagellate cyst without nucleic acid extraction steps, this method is more suitable for the identification of more than two cysts and does not apply to the identification of single dinoflagellate cyst. Because of the morphological plasticity of dinoflagellate cysts and the overlap morphological characteristics of cysts, the cysts belonging to different species are mistakenly treated as the same kind of cyst for PCR amplification at the same time, which eventually leads to the inaccuracy or failure of molecular identification. Therefore, rapid molecular identification technique of the single-cyst without nucleic acid-free extraction and cyst germination still obstacles to the exact molecular identification of cysts.